1. Field of the Invention
The present invention relates to electrical circuits. More specifically, the present invention relates to electrical circuits having a differential structure that uses complementary devices for processing single-ended signals.
2. Background Information
A circuit may be designed to have either single-ended or differential structure, both in the analogue and digital circuit application. The single-ended structure is the structure of a circuit having paired terminals, where only one of the terminals is connected either input or output terminal. In comparison with the single-ended structure, double-ended structure is known in the art. The double-ended structure is the structure of a circuit having paired terminals, where both of the paired terminals are connected to a single input or output terminal. A differential pair structure is well known in the art as an example of the double-ended structure. Differential pair structure is the structure of a circuit having double-ended structure where signal is differentially inputted and processed to and in the circuit.
A single-ended structure consumes relatively low power and produces relatively low noise. However, when a single-ended structure circuit is operating in class A or AB mode, the circuit may suffer from clamping of signal, which results in harmonic component problem.
On the other hand, differential pair circuit is not vulnerable to the interference problem. The reason is that AC current, which is not provided from power source circulates only through the circuit. Since differential pair circuit is not susceptible to the interference problem, it is advantageously used in integrating a lot of system blocks into one chip. Further, differential pair circuit is used in mixers which generally requires high level of isolation among radio frequency, local oscillation, and intermediate frequency signals.
Moreover, since differential pair circuit has symmetrical structure, even order distortion may be reduced. Because of the characteristic of reduced even order distortion, differential pair circuit is widely employed in amplifiers and mixers provided in the direct conversion receivers, which suffers from DC offset problem and, therefore, requires relatively high level of rejection characteristic of second order distortion.
There have been a lot of approaches for incorporating the advantageous characteristics of the single-ended and differential pair structures, in the analogue and digital circuit applications.
Especially in the RF circuit field, in order to use the combination of the single-ended and differential circuits, balun (balance unbalance) circuitry was necessarily used for converting single-ended signal to differential signal or differential signal to single-ended one. Balun circuitry may be made from either passive or active devices. However, when balun circuitry is made of passive devices, size of balun circuitry becomes large and, therefore, it is not easy to integrate balun circuitry in a chip. When balun circuitry is made of active devices, relatively large power consumption of the balun circuitry becomes problem especially in the RF circuit applications. Additionally, noise generated by active balun decreases signal to noise ratio.
In order to overcome this problem, it was suggested that differential pair circuitry is integrated in a chip while passive balun circuitry is provided on a PCB, thereby connecting the differential pair circuitry in the chip to the balun circuitry on the PCB. This method, however, is disadvantageous in that the passive balun circuitry has large size and manufacturing cost becomes high.
As another attempts to integrate the single-ended circuitry and differential pair circuitry in a single chip, integration of active balun circuitry in a chip has also been tried. This method, however, suffers from DC power consumption and added noise of the active balun circuitry.
In view of the above, there exists a need for a single-ended differential circuit that uses complimentary devices that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
An object of the invention is to provide a circuit for processing signals from single-ended structure by using differential pair circuitry having complementary devices.
Another object of the present invention is to provide RF mixing circuit having differential pair structure by using complementary devices which can process signals from single-ended structure.
The other object of the present invention is to provide cascode amplifier circuit, which has complementarily and symmetrically connected differential pair structure by using complementary devices, thereby being able to process signals from single-ended structure.
In order to accomplish the objects, the present invention provides a single-ended differential circuit comprising: first and second complementary devices having first, second, and third terminals, respectively, wherein current flowing from the second terminal to the third terminal has its quantity and direction being varying in dependant on the voltage driven to the first terminal, wherein the currents flowing through the first and second complementary devices vary in opposite relationship; an input terminal connected to the first terminals of the first and second complementary devices; and biasing means connected to the first, second and third terminals of the first and second devices, for determining biasing points of the first and second complementary devices such that the first and second devices operates in a differential relationship with respect to a signal driven to the input terminal, wherein the biasing means determining the biasing points such that one of the first and second devices is substantially active.
In accordance with another aspect of the invention, a single-ended differential RF mixer circuit is provided, The single-ended differential RF mixer comprises: first and second complementary devices having first, second, and third terminals, respectively, wherein current flowing from the second terminal to the third terminal has its quantity and direction being varying in dependant on the voltage driven to the first terminal, wherein the currents flowing through the first and second complementary devices vary in opposite relationship; an input terminal connected to the first terminals of the first and second complementary devices; and biasing means connected to the first, second and third terminals of the first and second devices, for determining biasing points of the first and second complementary devices such that the third terminals of the first and second complementary devices are maintained at a predetermined voltage value with respect to the second terminals of the first and second complementary devices and wherein impedance values at the third terminals vary in accordance with variation of a signal driven to the first terminals of the first and second complementary devices, when the first and second complementary devices are biased such that voltage values at the second and third terminals are adjusted to a predetermined value.
In accordance with other aspect of the invention, a single-ended differential RF mixer circuit is provided. The single-ended differential RF mixer circuit comprises: first complementary unit having first and second complementary devices which have first, second, and third terminals, respectively, wherein current flowing from the second terminal to the third terminal has its quantity and direction being varying in dependant on the voltage driven to the first terminal, wherein the currents flowing through the first and second complementary devices vary in opposite relationship; second complementary unit having third and fourth complementary devices which have first, second, and third terminals, respectively, wherein current flowing from the second terminal to the third terminal has its quantity and direction being varying in dependant on the voltage driven to the first terminal, wherein the currents flowing through the first and second complementary devices vary in opposite relationship; first input terminal connected to the first terminals of the first and second complementary devices; second input terminal connected to the first terminals of the third and fourth complementary devices; and biasing means connected to the first, second and third terminals of the first and second devices, for determining biasing points of the first and second complementary devices such that the third terminals of the first and second complementary devices are maintained at a predetermined voltage value with respect to the second terminals of the first and second complementary devices and for determining biasing points of the third and fourth complementary devices such that the third terminals of the third and fourth complementary devices are maintained at a predetermined voltage value with respect to the second terminals of the third and fourth complementary devices, and wherein impedance values at the third terminals vary in accordance with variation of a signal driven to the first terminals of the first through fourth complementary devices, when the first through fourth complementary devices are biased such that voltage values at the second and third terminals are adjusted to a predetermined value.
In accordance with other aspect of the invention, a single-ended differential amplifier circuit is provided. The single-ended differential amplifier circuit comprises: first unit having first and second active devices which have first, second, and third terminals, respectively, wherein current flowing from the second terminal to the third terminal has its quantity and direction being varying in dependant on the voltage driven to the first terminal; second unit having third and fourth devices which have first, second, and third terminals, respectively, wherein current flowing from the second terminal to the third terminal has its quantity and direction being varying in dependant on the voltage driven to the first terminal; and biasing means connected to the first terminals of the first and third active devices and an input terminal, and connected to the second terminals of the second and fourth active devices and an output terminal, for determining biasing points of the first and second units such that the first and second units operates in a differential relationship with respect to a signal driven to the input terminal, wherein the biasing means determines the biasing points such that one of the first and second units is substantially active.
These and other objects, features, aspects, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.